(1) Field of the Invention
The present invention relates to a plastic functional element having memory function and operational function controlled by at least one of light and electric field, and more particularly to an organic memory element and organic operational element.
(2) Description of the Prior Art
In the field of an element comprising an organic membrane provided with a memory function and a switching function controllable by both light irradiation and electric field, elements which is based on insulator-metal transition resulting from doping of conducting polymer has been already invented and established. In this case, as the method for controlling doping process by light or electric field, an electro-chemical method using solid electrolyte or electrolyte aqueous solution or optical dissociation of solid electrolyte can be used. Then the conducting polymer can be used for a memory element and a switching element based on remarkable change in the absorption spectra and conductivity due to insulator-metal transition by doping.
FIG. 1 shows an example for describing the structure of the above mentioned organic optical memory element or the organic optical switching element based on doping to conducting polymer proposed by Katsumi Yoshino et al on Japanese Journal of Applied Physics, vol. 24, p. L373, 1985.
In the figure, the electrode 1 comprising an Indium-Tin coated glass plate, a conducting polymer membrane 2 of polyacetylene, a polymer matrix membrane 13 of polystyrene or the like containing triphenylsulfonium hexafluoroarsenate salt or the like, and a transparent electrode 4 comprising Indium-Tin coated quartz plate are shown.
Then the operation of this type of element shown in FIG. 1 is described. Upon the irradiation of light 5 with the wave length ranging from visible to ultraviolet from a Hg lamp onto the element, triphenylsulfonium hexafluoroarsenate salt contained in the polymer membrane 3 is optically dissociated, hexafluoroarsenate ions are doped on the polyacetylene in the conducting polymer membrane 2, and color changes from red to blue. The blue color is maintained for three months or more under an open circuit condition in air. By applying a negative bias voltage (1.2 V) on the polyacetylene of the conducting polymer membrane 2, the hexafluoroarsenate ions doped in the polyacetylene are electrochemically dissociated and the color turns to red again. Based on this mechanism, the element can be used as an erasable optical memory.
Then by applying a positive bias voltage on the conducting polymer membrane 2 of polyacetylene, triphenylsulfonium hexafluoroarsenate salt in the polymer membrane 3 is electrically dissociated to dope hexafluoroarsenate ions in the conducting polymer membrane 2 of polyacetylene, and the color changes from red to blue. By short-circuiting or applying a negative bias voltage on the conducting polymer membrane 2 of polyacetylene, the color changes from blue to red on the same reason as mentioned above. Based on this mechanism, a switching element controllable with light irradiation and electric field is provided.
Because the conventional organic memory element or the organic switching element is based on the doping of carriers caused from ion transfer as described above, the writing and reading time is limited when this element is used as a memory element and the switching time for a switching element is limited. In addition, since this type of element can not be made small in size due to the material properties of polymer, the element has some limitation to use for an integrated circuit due to these difficulties.